The present invention relates to blood filters that are used in extra corporeal blood circuits. More particularly, the invention is directed to arterial blood filters used during heart bypass surgery for the removal of particulate matter and gaseous emboli from blood that has been oxygenated and is being returned to the patient.
Blood filters are used for the treatment and filtration of blood for various applications such as cardiopulmonary bypass techniques, blood transfusions, dialysis treatment etc. Arterial blood filters are provided to trap and remove particulate matter and undissolved gaseous emboli from oxygenated blood. Typically, the arterial blood filter is one of the components in an extra corporeal blood circuit in which blood flows from a patient, through a cardiotomy reservoir, an oxygenator and finally into the arterial filter before it is returned to the patient. The arterial blood filter may be the last component of the blood flow circuit through which the blood flows before the blood is returned to the patient, and thus this filter must be durable, reliable and effective in the filtration process.
Arterial blood filters are disposable after a single patient use and must be designed for manufacture, packaging and sterilization at minimal cost. Use of low cost materials and minimization of the amount of materials is critical to the effective manufacture of an arterial filter along with simple, conventional tooling and assembly processes. A small concise design is also a critical factor in packaging costs, efficient sterilization and storage space costs related to the filter. The extra corporeal circuit, including the arterial filter, must be primed with a suitable fluid to remove air from the system prior to the introduction of blood flow; and it is therefore important that the filter have a concise internal volume to minimize priming fluid and priming time in preparation for use.
An example of an early arterial filter having a hollow tubular housing containing a concentric cylindrical filter element is shown in U.S. Pat. No. Re. 32,711 (reissue of U.S. Pat. No. 4,411,783) to Dickens et al. assigned to Shiley Inc. This patent discloses a large diameter cover on the top of the filter element having a symmetrically positioned frusto-conically shaped dome. Blood is introduced tangentially into the upper end of the device and flows over and around the dome then downwardly and through the filter element. The symmetrically positioned dome tends to produce some obstruction to the inlet of blood into the filter, and the flow over the dome tends to create some turbulence and re-circulation with the incoming flow of new blood. The inlet chamber includes a large space for re-circulation and de-bubbling of the blood and results in a relatively large internal volume that requires priming. This early design was considered to be a significant advancement over the prior art at that time, and has been widely used.
Another example of a related prior art arterial filter is described in U.S. Pat. No. 4,919,802 to Katsura, assigned to Terumo Inc. This patent discloses a tubular cylindrical housing with a concentric cylindrical filter element having a symmetrically positioned frusto-conically shaped dome similar to the device of Dickens et al. This patent particularly teaches a horizontally extended tubular blood inlet, adjacent to the cylindrical housing, to introduce blood tangentially into the upper chamber around the side of the symmetrically positioned dome to avoid any obstruction of blood flow by the dome. This patent describes improved performance in de-bubbling and laminar blood flow that does not damage any platelets of the blood cells during the filtering process. The expanded diameter inlet path would seem to require a much larger top cap resulting in more material, a more complex design, complex tooling and assembly for manufacture, and resulting in more external and internal volume and larger packaging and priming requirements.
Another example of a related prior art patent is disclosed in U.S. Pat. No. 5,632,894 to White et al., assigned to Gish Biomedical, Inc. This patent incorporates a tubular housing with a cylindrical filter element having a symmetrically positioned frusto-conically shaped dome similarly to the filter described in the Dickens et al. patent. This patent discloses a tangential tubular blood inlet extended horizontally and adjacent to the side of the housing similarly to the device described in the Katsura patent; and further teaches improves performance by inclining the tubular inlet at an angle, so that the blood is introduced into the filter around the side of the dome and at an upward angle to enhance flow within the filter device. This improvement seems to include the complexity, material and volume requirements as discussed in regard to device in the Katsura patent, plus the additional complexities and costs associated with the inclined inlet and flow path featured in the patent.
In view of the foregoing, it is an object of the present invention to provide a blood filter that has a smooth tangential inlet that is not obstructed by any internal components of the filter.
It is another object to provide a blood filter that provides smooth laminar flow in a downward spiraling vortex that provides efficient separation of any undissolved gases from the blood and does not produce any damage to the blood cells.
It is another object to provide a blood filter that is very compact having minimum external dimensions for efficient packaging and storage and minimal internal dimensions for a low priming volume and efficient blood flow.